The present invention relates to a reduced pressure type steam generator equipped with an air tight steam chamber or compartment which is maintained at reduced atmospheric pressure or vacuum conditions and within which there is contained a heat or heatable medium liquid, and at the top of the steam chamber there is provided a gas reservoir with an outlet covered with a polymer film for permeating out a non-condensible gas.
The so-called reduced pressure type or vacuum steam generator wherein water or another heatable medium is enclosed in the air tight vessel of the generator and wherein the heatable medium is heated by a heat source, such as gas or oil, and a heating pipe is introduced into the vessel in order to be indirectly heated by the vapors of the heatable medium and connected with a hot water supply tap or heating equipment, has certain advantages in that its handling is safer and its heat transfer is superior inasmuch as the vessel is operated at reduced pressure or vacuum conditions. However, such equipment also has certain drawbacks or limitations, such as the introduction of air at the joint locations between the vessel and auxiliary equipment or accessories or impaired heat transfer due to generation of non-condensible gas, such as hydrogen, by virtue of electro-chemical reactions. The introduction of air at the joints or joint locations can be prevented if adequate precautions are taken with respect to the construction of the joints or through appropriate selection of the packing material. However, it is extremely difficult to prevent the generation of hydrogen gas due to elecro-chemical reactions and a non-condensible gas such as hydrogen has heretofore been exhausted according to conventional techniques from the vessel within which such gas is generated by the use of a vacuum pump or ejector.